Vehicle occupant sensing system having sensor assemblies with variable blasing member

ABSTRACT

A vehicle occupant sensing system that includes a sensor assembly. The sensor assembly has a housing that includes a base and an upper slide member. The upper slide member is moveable toward and away from the base. A sensor is operatively fixed relative to at least one of the upper slide member and the base and is operable to detect movement of the upper slide member toward and away from the base. Additionally, the vehicle occupant sensing system includes a variable biasing member adapted to bias the upper slide member away from the base with a force that is non-linearly related to movement of the upper slide member toward and away from the base. The vehicle occupant sensing system of the present invention may be employed in a vehicle seat assembly to detect a condition of the vehicle seat assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 10/748,536,entitled “Vehicle Occupant Sensing System Having a Low Profile SensorAssembly” and filed Dec. 30, 2003, which is a continuation-in-part ofU.S. Ser. No. 10/606,649, entitled “Encapsulated Spring Sensor Assembly”and filed Jun. 26, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to vehicle occupant sensingsystems and, more particularly, to a vehicle occupant sensing systemhaving sensor assemblies with a variable biasing member.

2. Description of the Related Art

Automotive vehicles employ seating systems that accommodate thepassengers of the vehicle. The seating systems include restraint systemsthat are calculated to restrain and protect the occupants in the eventof a collision. The primary restraint system commonly employed in mostvehicles today is the seatbelt. Seatbelts usually include a lap belt anda shoulder belt that extends diagonally across the occupant's torso fromone end of the lap belt to a mounting structure located proximate to theoccupant's opposite shoulder.

In addition, automotive vehicles may include supplemental restraintsystems. The most common supplemental restraint system employed inautomotive vehicles today is the inflatable airbag. In the event of acollision, the airbags are deployed as an additional means ofrestraining and protecting the occupants of the vehicle. Originally, thesupplemental inflatable restraints (airbags) were deployed in the eventof a collision whether or not any given seat was occupied. Thesesupplemental inflatable restraints and their associated deploymentsystems are expensive and over time this deployment strategy was deemednot to be cost effective. Thus, there became a recognized need in theart for a means to selectively control the deployment of the airbagssuch that deployment occurs only when the seat is occupied.

Partially in response to this need, vehicle safety systems have beenproposed that include vehicle occupant sensing systems capable ofdetecting whether or not a given seat is occupied. The systems act as aswitch in controlling the deployment of a corresponding air bag. Assuch, if the occupant sensing device detects that a seat is unoccupiedduring a collision, it can prevent the corresponding air bag fromdeploying, thereby saving the vehicle owner the unnecessary cost ofreplacing the expended air bag.

Furthermore, many airbag deployment forces and speeds have generallybeen optimized to restrain one hundred eighty pound males because theone hundred eighty pound male represents the mean average for all typesof vehicle occupants. However, the airbag deployment force and speedrequired to restrain a one hundred eighty pound male exceeds that whichare required to restrain smaller occupants, such as some females andsmall children. Thus, there became a recognized need in the art foroccupant sensing systems that could be used to selectively control thedeployment of the airbags when a person below a predetermined weightoccupies the seat.

Accordingly, other vehicle safety systems have been proposed that arecapable of detecting the weight of an occupant. In one such air bagsystem, if the occupant's weight falls below a predetermined level, thenthe system can suppress the inflation of the air bag or will prevent theair bag from deploying at all. This reduces the risk of injury that theinflating air bag could otherwise cause to the smaller-sized occupant.

Also, many airbag deployment forces and speeds have generally beenoptimized to restrain a person sitting generally upright towards theback of the seat. However, the airbag deployment force and speed mayinappropriately restrain a person sitting otherwise. Thus, there becamea recognized need in the art for a way to selectively control thedeployment of an airbag depending on the occupant's sitting position.

Partially in response to this need, other vehicle safety systems havebeen proposed that are capable of detecting the position of an occupantwithin a seat. For example, if the system detects that the occupant ispositioned toward the front of the seat, the system will suppress theinflation of the air bag or will prevent the air bag from deploying atall. This reduces the risk of injury that the inflating air bag couldotherwise cause to the occupant.

It can be appreciated that these occupant sensing systems providevaluable data, allowing the vehicle safety systems to function moreeffectively to reduce injuries to vehicle occupants.

One necessary component of each of the known systems discussed aboveincludes some means for sensing the presence of the vehicle occupant inthe seat. One such means may include a sensor device supported withinthe lower seat cushion of the vehicle seat. For example, U.S. publishedpatent application having U.S. Ser. No. 10/249,527 and Publication No.US2003/0196495 A1 filed in the name of Saunders et al. discloses amethod and apparatus for sensing seat occupancy including asensor/emitter pair that is supported within a preassembled one-piececylinder-shaped housing. The housing is adapted to be mounted within ahole formed in the seat cushion and extending from the B-surface towardthe A-surface of the seat cushion. The sensor/emitter pair supported inthe housing includes an emitter that is mounted within the seat cushionand spaced below the upper or A-surface of the seat cushion. Inaddition, the sensor is also supported by the housing within the seatcushion but spaced below the emitter. The cylindrical housing is formedof a compressible, rubber-like material that is responsive to loadsplaced on the upper surface of the seat cushion. The housing compressesin response to a load on the seat cushion. The load is detected throughmovement of the emitter toward the sensor as the housing is compressed.The housing is sufficiently resilient to restore the emitter to fullheight when no load is applied to the upper surface of the seat cushion.The Saunders et al. system also includes a processor for receiving thesensor signals and interpreting the signals to produce an output toindicate the presence of an occupant in the seat.

While the Saunders et al. occupant seat sensing system teaches asensor/emitter pair that may sense the presence of a vehicle seatoccupant, it suffers from certain disadvantages associated with the factthat it is mounted within the seat cushion of the vehicle seat. Forexample, vehicle seat cushions typically employ a foam or other cushionymaterial of a predetermined thickness. The thickness of this material ispreferably calculated to provide adequate comfort for the occupant.However, with the housings of the sensor/emitter pairs mounted withinthe cushion, the occupant may feel one or more of the housings throughthe seat cushion. This is especially true over time as the seat cushionbecomes worn. Furthermore, while the compressible, rubber-like housingtaught by Saunders et al. is generally responsive to forces extendingalong the length of its axis, is also subject to transverse or “shear”forces acting through the seat cushion. Thus, the housing can bedeformed in an irregular manner resulting in false readings generated bythe sensor/emitter pair.

Therefore, there is an ongoing need in the art for a vehicle occupantsensing system including a low profile sensor assembly that can providesuitable occupant sensing capabilities and yet be positioned outside theenvelope defined by the lower seat cushion without detrimentallyaffecting the comfort level of the seat. Furthermore, there is a need inthe art for such a vehicle occupant sensing system that is resistant toshear forces and otherwise constructed to respond in a single axis ofmovement.

Furthermore, the stiffness of the housing of the Saunders et al. devicecan disadvantageously limit the system's responsiveness. For instance,if a lighter occupant sits on the seat cushion, an overly stiff housingmay not deflect enough and thereby inhibit the sensor/emitter pair fromgenerating a responsive signal. As such, the system cannot gather datafor occupants that are at or below a certain weight limit. On the otherhand, if a heavier occupant sits on the seat cushion, an overly elastichousing may deflect too much, allowing the sensor and emitter to contacteach other. As such, the system cannot distinguish between occupantsthat are at or above a certain weight limit, and contact between thesensor and emitter can cause premature wear.

Overall, the system may not appropriately sense the presence of someoccupants because of these limitations in system responsiveness.Accordingly, there remains a need in the art for a vehicle occupantsensing system that is responsive to a wider occupant weight range.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages in the related art ina vehicle occupant sensing system that includes a sensor assembly. Thesensor assembly has a housing that includes a base and an upper slidemember. The upper slide member is moveable toward and away from thebase. A sensor is operatively fixed relative to at least one of theupper slide member and the base and acts to detect movement of the upperslide member toward and away from the base. Additionally, the vehicleoccupant sensing system includes a variable biasing member adapted tobias the upper slide member away from the base with a force that isnon-linearly related to movement of the upper slide member toward andaway from the base. The vehicle occupant sensing system of the presentinvention may be employed in a vehicle seat assembly to detect acondition of the vehicle seat assembly.

The variable biasing member preferably exhibits an appropriate stiffnessfor both lighter and heavier occupants of the vehicle seat assembly. Forinstance, when a lighter occupant sits on the seat assembly, thevariable biasing member preferably deflects enough to cause correlatingdata to be generated. However, when a heavier occupant sits on the seatcushion, the variable biasing member is preferably stiff enough to allowdeflection without the variable biasing member reaching a solid height,thereby allowing correlating data to be further generated. Thus, thevariable biasing member allows data to be generated for lighteroccupants and for heavier occupants, thereby making the vehicle occupantsensing system more responsive to a wider occupant weight range.

Other features and advantages of the present invention will be readilyappreciated, as the same becomes better understood, after reading thesubsequent description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a vehicle seat assembly incorporating avehicle occupant sensing system having a plurality of low profile sensorassemblies;

FIG. 2 is an exploded view of one embodiment of the low profile sensorassembly suitable for use in the vehicle occupant sensing systemillustrated in FIG. 1;

FIG. 3 is a cross-sectional side view of the low profile sensor assemblyof FIG. 2 shown in a free state;

FIG. 4 is a cross-sectional side view of the low profile sensor assemblyof FIG. 2 shown in a compressed state;

FIG. 5 is an exploded view of another embodiment of the low profilesensor assembly suitable for use in the vehicle occupant sensing systemillustrated in FIG. 1;

FIG. 6 is a cross-sectional side view of the low profile sensor assemblyof FIG. 5 shown in a free state;

FIG. 7 is a cross-sectional side view of the low profile sensor assemblyof FIG. 5 shown in a compressed state;

FIG. 8 is a side view of one embodiment of a variable biasing member ofthe present invention; and

FIG. 9 is a graph depicting response from one embodiment of the variablebiasing member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, where like numerals are used to designatelike structure throughout the figures, an exploded view of oneembodiment of the vehicle seat assembly of the present invention isgenerally indicated at 10 in FIG. 1. The vehicle seat assembly 10includes a seat back, generally indicated at 12, and a lower seatassembly, generally indicated at 14. The lower seat assembly 14 has aseat cushion 16 that defines an upper surface 18, and a lower surface 20that is spaced from the upper surface 18. The upper surface 18 of theseat cushion 16 may be referred to as the “A-surface” and the lowersurface 20 may be referred to as the “B-surface.” The seat cushion 16also defines an inboard side 22 and an outboard side 24. When anoccupant (not shown) is supported on the lower seat assembly 14, theweight of the occupant will apply an axial load directed generallythrough the upper surface 18 of the seat cushion 16 toward the lowersurface 20. Although the weight of the occupant will induce an axial aswell as shear forces in the seat cushion 16, those having ordinary skillin the art will recognize that the primary load path of the occupant'sweight will be substantially vertical from the upper surface 18 towardthe lower surface 20, through the seat cushion 16.

The lower seat assembly 14 also includes a seat pan, generally indicatedat 26. The seat pan 26 is generally disposed beneath the lower surface18 so as to support the seat cushion 16. In turn, the seat pan 26 isoperatively supported relative to the floor of the vehicle using anysuitable structure of the type commonly known in the art, such as a seattrack (not shown). In addition, the vehicle seat assembly 10 includes avehicle occupant sensing system, generally indicated at 28. The vehicleoccupant sensing system 28 is used for detecting a condition of thevehicle seat assembly 10, such as whether or not the vehicle seatassembly 10 is occupied, whether the occupant is above or below acertain weight requirement, or whether the occupant is sitting in acertain position.

The sensing system 28 includes a circuit carrier tray, generallyindicated at 30, that is supported by the seat pan 26. The circuitcarrier tray 30 includes a plurality of resilient attachment tabs 32extending upward toward the lower surface 20 of the lower seat cushion16. Each attachment tab 32 is shaped like a partial ring that extendsupward from the tray 30. In the preferred embodiment illustrated in FIG.1, the attachment tabs 32 are arranged into mirror-image pairs spacedintermittently about the tray 30. The tray 30 supports components of thevehicle occupant sensing system 28 as will be described in greaterdetail below.

The vehicle occupant sensing system 28 also includes a circuit carrier34, which is disposed adjacent the lower surface 20 of the seat cushion16. The tray 30 supports the circuit carrier 34, and the circuit carrier34 includes a plurality of cutouts 36 each having a shape correspondingto the shape of the attachment tabs 32 of the tray 30 such that the tabs32 can extend upward through the circuit carrier 34.

The vehicle occupant sensing system 28 also includes an electric circuit38, which is supported by the circuit carrier 34. Specifically, thecircuit carrier 34 is made of a thin nonconductive andcorrosion-resistant material, and it encapsulates known electricalcomponents that form the electric circuit 38. For instance, in oneembodiment, a flexible printed circuit forms the circuit carrier 34 andelectric circuit 38.

The circuit 38 is electrically connected to a controller schematicallyillustrated at 40. As described in greater detail below, the electriccircuit 38 carries electric signals generated by the vehicle occupantsensing system 28 to the controller 40. The controller 40 iselectrically attached to a restraint system, schematically illustratedat 42. The restraint system 42 can be of many types, such as an air bagsystem, and the controller 40 sends output to the restraint system 42based on the signals delivered by the electric circuit 38. Although anairbag restraint system is discussed here, one having ordinary skill inthe art will recognize that the type of restraint system 42 connected tothe controller 40 does not limit the scope of the present invention.

The system 28 also includes a plurality of low profile sensor assemblies44 that are supported by the tray 30, below the lower surface 20 of theseat cushion 16. In one embodiment not shown, the lower surface 20includes a plurality of depressions, and each of the low profile sensorassemblies 44 are spaced according to a corresponding depression formedin the lower surface 20 of the lower seat cushion 16. As will bediscussed in greater detail below, the sensor assemblies 44 have arelatively low profile and can collapse in a more compact manner thansimilar sensor assemblies of the prior art. Advantageously, these lowprofile sensor assemblies 44 allow an occupant to sit more comfortablyupon the vehicle seat 10.

Also, a sensor, generally indicated at 46, is operatively fixed relativeto each of the low profile sensor assemblies 32. The sensor 46 is inelectrical communication with the electric circuit 38. The low profilesensor assemblies 44 each cooperatively operate with the associatedsensor 46 to detect a condition of the vehicle seat 10 as will bedescribed in greater detail below. For example, the low profile sensorassemblies 44 and sensor 46 can operate to detect that the vehicle seat10 is unoccupied, is occupied by a person of a particular weight, or isoccupied by a person sitting in a particular position.

One embodiment of the low profile sensor assembly is generally indicatedat 44 and shown in greater detail in FIGS. 2-4. The low profile sensorassembly 44 generally includes a housing 48, having a base 50, an upperslide member 52, and an intermediate guide member 54 disposed betweenthe upper slide member 52 and the base 50. The upper slide member 52 andthe intermediate guide member 54 are both supported for movement towardand away from the base 50. A biasing member 56 acts to bias the upperslide member 52 and intermediate guide member 54 away from the base 50as will be described in greater detail below.

In the preferred embodiment illustrated in these figures, the base 50includes a base guide 58, which is shaped like a hollow tube so as todefine a wall 60 with a bore 62 extending axially therethrough. On anoutside surface of the wall 60, two hold-down flanges 64 projectradially outward, spaced 180° apart from each other. An aperture 66extends radially through the wall 60 directly above each hold-downflange 64.

The base 50 also includes a retainer 68, which is substantiallydisc-shaped and is attached to one terminal end of the base guide 58.Two resilient tabs 70 extend radially and upward from an outercircumferential edge of the retainer 68. The tabs 70 are spaced 180°apart from each other. To connect the retainer 68 and the base guide 58,the retainer 68 moves axially into the bore 62 of the base guide 58 suchthat the tabs 70 of the retainer 68 snap into the apertures 66 of thebase guide 58.

As shown in FIGS. 3 and 4, the base 50 can be attached to the annularattachment tabs 32 that extend upwardly from the tray 30. Specifically,the hold-down flanges 64 of the base guide 58 can be positioned underthe annular attachment tabs 32 of the tray 30 such that the annularattachment tabs 32 retain the hold-down flanges 64. In one embodiment,to attach the base 50 to the tray 30, the bottom surface of the base 50is positioned on the tray 30 such that the hold-down flanges 64 and theannular attachment tabs 32 are not aligned. Then, the base 50 is rotatedabout its axis until the hold-down flanges 64 move completely under theannular attachment tabs 32. In another embodiment, the hold-down flanges64 and the annular attachment tabs 32 are aligned, and the base 50 ismoved axially toward the tray 30 such that the annular attachment tabs32 bend back and snap over the hold-down flanges 64.

Also, an annular void 72 is formed near the axial center of the base 50.In one embodiment shown in FIGS. 3 and 4, the sensor 46 is a Hall effectsensor attached to the circuit carrier 34 between each pair of tabs 32of the tray 30. Electrical attachment between the sensor 46 and thecircuit carrier 34 can be accomplished in the manner described inapplicant's co-pending application, Ser. No. 10/748,514, entitled“Vehicle Occupant Sensing System and Method of Electrically Attaching aSensor to an Electrical Circuit,” which is hereby incorporated in itsentirety by reference. When the base 50 is attached to the tray 30, theannular void 72 provides clearance for the sensor 46.

The retainer 68 has a top surface 74, which is stepped so as define aplurality of concentric features. First, the stepped top surface 74defines an outer step 76 formed on the outer radial portion of the topsurface 74 of the retainer 68. Next, the stepped top surface 74 definesan inner platform 78 formed radially inboard of the outer step 76. Asshown in FIGS. 3 and 4, the inner platform 78 extends axially upwardfrom the outer step 76. Finally, nearest the center of the stepped topsurface 74 is a ring 80 extending upward from the inner platform 78.

As noted above, the low profile sensor assembly 44 includes an upperslide member 52. The upper slide member 52 includes an upper discportion 82 and a support wall 84 extending axially downward from theouter circumference of the upper disc portion 82. The support wall 84has a smaller diameter than the diameter of the intermediate guidemember 54 such that the upper slide member 52 can move axially throughthe intermediate guide member 54. The biasing member 56 is disposedbetween the inner platform 78 of the base 50 and the upper disc portion82 of the upper slide member 52.

As noted above, the low profile sensor assembly 44 also includes theintermediate guide member 54, which is substantially tubular so as todefine an outer surface 56 and an inner surface 88. The diameter of theintermediate guide member 54 is smaller than the diameter of the bore 62of the base guide 58 such that the intermediate guide member 54 can moveaxially through the bore 62.

The intermediate guide member 54 includes a lower flange 90 formed onits lower end, and the base 50 includes an upper flange 92 formed on theupper end of the base guide 58. In the embodiment shown, the lowerflange 90 of the intermediate guide member 54 extends radially outward,and the upper flange 72 of the base 50 extends radially inward. Thediameter of the lower flange 90 is larger than the diameter of the upperflange 92. As such, the intermediate guide member 54 can be positionedwithin the bore 62 of the base guide 58. As the lower flange 90 of theintermediate guide member 54 slides toward the upper flange 92, theupper flange 92 interferes with the lower flange 90, thereby inhibitingfurther upward movement of the intermediate guide member 54. Thus, theupper flange 92 on the base 50 and the lower flange 90 on theintermediate guide member 54 cooperate to define the limit of slidingmovement of the intermediate guide member 54 away from the base 50.

While the upper flange 92 of the base 50 defines one limit of travel ofthe intermediate guide member 54, the outer step 76 of the base 50defines the other limit of travel. As shown specifically in FIG. 4, theintermediate guide member 54 can move axially downward within the base50 until the lower flange 90 of the intermediate guide member 54contacts the outer step 76 of the base 50. Thus, the outer step 76 isadapted to accept the lower flange 90 of the intermediate guide member54 when the intermediate guide member 54 moves toward the base 50, andit defines the axial limit of travel of the intermediate guide member 54toward the base 50. It is noted that since the outer step 76 is formedat a lower level than the inner platform 78 of the base 50, theintermediate guide member 54 has a greater range of motion in the axialdirection. As such, the sensor assembly 44 has a lower profile thanother sensors known in the related art and can collapse into a morecompact arrangement, thereby making the sensor assembly 44 less likelyto detrimentally affect the comfort of the vehicle seat 10.

In the preferred embodiment, the base 50 defines an inner guide surface94. The inner guide surface 94 is formed on the inner surface of thewall 60 of the base guide 58, and it has a diameter slightly larger thanthe diameter of the lower flange 90 of the intermediate guide member 54.The inner guide surface 94 substantially guides the lower flange 90 asit slides within the base 50, such that the intermediate guide member 54slides in a substantially axial direction. Thus, the lower flange 90 ofthe intermediate guide member 54 cooperates with the inner guide surface94 of the base 50 to facilitate movement of the intermediate guidemember 54 relative to the base 50 in a substantially axial direction. Byguiding the intermediate guide member 54 in a substantially axialdirection, the sensor 46 is adapted to generate more accurate readingsas will be described in greater detail below.

The upper slide member 52 includes a lower flange 96 formed on its lowerend. On the other hand, the intermediate guide member 54 includes anupper flange 98 formed on its upper end. In the embodiment shown, thelower flange 96 of the upper slide member 52 extends radially outward,and the upper flange 98 of the intermediate guide member 54 extendsradially inward. The diameter of the lower flange 96 is larger than thediameter of the upper flange 98. As such, the upper slide member 52 canbe positioned within the intermediate guide member 54. As the lowerflange 96 of the upper slide member 52 slides toward the upper flange 98under the influence of the biasing force generated by the biasing member56, the upper flange 98 interferes with the lower flange 96, therebyinhibiting further upward movement of the upper slide member 52. Thus,the upper flange 98 on the intermediate guide member 54 and the lowerflange 96 on the upper slide member 52 cooperate to define the limit ofsliding movement of the upper slide member 52 away from the base 50.

While the upper flange 98 of the intermediate guide member 54 definesone limit of travel of the upper slide member 52, the inner platform 78on the retainer 68 of the base 50 defines the other limit of travel. Asshown specifically in FIG. 4, the upper slide member 52 can move in thedirection of the base 52 in response to the presence of an occupant ofthe seat assembly 10 and against the biasing force of the biasing member50 until the lower flange 96 of the upper slide member 52 contacts theinner platform 78 of the base 50. Thus, the inner platform 78 is adaptedto accept the lower flange 96 of the upper slide member 52 when theupper slide member 52 moves toward the base 50, and it defines the axiallimit of travel of the upper slide member 52 toward the base 50.

Also, in the preferred embodiment, the intermediate guide member 54defines an inner guide surface 100. The inner guide surface 100 isformed on the inner surface 88 of the intermediate guide member 54, andit has a diameter slightly larger than the diameter of the lower flange96 of the upper slide member 52. The inner guide surface 100substantially guides the lower flange 96 as it slides within theintermediate guide member 54, such that the upper slide member 52 slidesin a substantially axial direction. Thus, the lower flange 96 of theupper slide member 52 cooperates with the inner guide surface 100 of theintermediate guide member 54 to facilitate movement of the upper slidemember 52 relative to the intermediate guide member 54 in asubstantially axial direction. By guiding the upper slide member 52 in asubstantially axial direction, the sensor 46 is adapted to generate moreaccurate readings as will be described in greater detail below.

Furthermore, the upper slide member 52 includes a retainer 102 extendingin the general direction of the base 50. In the embodiment shown, theretainer 102 is cup-shaped and extends from the center of the upper discportion 52 of the upper slide member 52 in the direction of the base 50so as to be axially aligned with the sensor 46. In the embodiment shownin FIGS. 3 and 4, an emitter 104, such as a magnet, is operativelycontained in and supported by the retainer 102.

Additionally, the base 50 defines a receptacle 106 formed along theaxial center of the base 50 so as to be aligned with the retainer 102.As shown specifically in FIG. 4, the receptacle 106 is adapted toreceive the retainer 102 when the upper slide member 52 has moved towardthe base 50. Since the retainer 102 is able to fit within the receptacle106, the upper slide member 52 can move further downward within the base50, allowing the low profile sensor assembly 44 to collapse into a morecompact arrangement. Advantageously, the low profile sensor assembly 44is less likely to detrimentally affect the comfort of the vehicle seat10.

In the embodiment shown here, the biasing member 56 is partiallydisposed about the ring 80 of the base 50 as well as about the retainerof the upper slide member 52. As noted above, the biasing member 56 isadapted to bias the upper slide member 52 and the intermediate guidemember 54 away from the base 50 until the lower flanges 90, 96 contactthe corresponding upper flanges 92, 98, respectively. However, while thebiasing member 56 employed for the preferred embodiment disclosed hereinis a coiled spring, those having ordinary skill in the art willappreciate that any suitable biasing member may be employed to bias theupper slide member 52 and, in turn, the intermediate guide member 54away from the base 50.

Thus, the weight of an occupant will deform the seat cushion 16 suchthat the lower surface 20 of the lower seat cushion 16 pushes the upperslide member 52 toward the base 50. As the upper slide member 52 moves,the sensor 46 detects an increase in magnetic flux density generated bythe approaching emitter 104. In this way, the sensor 46 is operable todetect movement of the upper slide member 52 toward and away from thebase 50. In turn, the sensor 46 generates a responsive signal indicativeof the increase in flux density, and the controller 40 sends output tothe restraint system 42 based on these signals. As stated, the guidesurfaces 94, 100 direct the intermediate guide member 54 and the upperslide member 52 in a substantially axial direction. As such, an emitter104 maintains a constant direction of travel relative to the sensor 46,thereby inhibiting the sensor 46 from obtaining false readings.

Those having ordinary skill in the art will appreciate that the sensor46 could be fixed to the upper guide member 52 and the emitter 104 couldbe fixed under the base 50 without departing from the spirit of theinvention. In other words, the sensor 46 may be operatively fixedrelative to at least one of the upper slide member 52 and the base 50such that the sensor 46 detects movement of the upper slide member 52toward and away from the base 50.

Importantly, several features of the low profile sensor assembly 44allow it to collapse in a more compact manner. Specifically, the outerstep 76 of the base 50 allows the intermediate guide member 54 to travellower into the base 50, and the receptacle 106 in the base 50 allows theretainer 102 and thus the upper slide member 52 to move further into thebase 50 for increased collapsibility. Furthermore, the intermediateguide member 54 allows the upper slide member 52 to move substantiallywithin the base 50. These features allow the fully compressed height ofthe low profile sensor assembly 44 to be relatively small. For instance,in one embodiment, the fully extended height of the sensor assembly 44is 17 mm and the fully-compressed height is approximately 10 mm.Advantageously, because it can be made more compact, the low profilesensor assembly 44 is less likely to detrimentally affect the comfort ofthe vehicle seat 10.

While the sensor assembly 44 illustrated in FIGS. 2-4 provides a lowprofile and improved collapsibility while employing a singleintermediate guide member 54, those having ordinary skill in the artwill appreciate that the present invention is not limited to a singleintermediate guide member 54. Rather, those having ordinary skill in theart will appreciate that the low profile sensor assembly 44 of thepresent invention may include more than one intermediate guide member 54as a means of further reducing the profile of the low profile sensorassembly 44.

Turning now to FIGS. 5 through 7, a second embodiment of a low profilesensor assembly is generally indicated at 244 where like numeralsincreased by 200 are used to designate like structure with respect tothe embodiment illustrated in FIGS. 2 through 4. The sensor assembly 244can be included in the vehicle seat assembly 10 of FIG. 1.

As shown, the low profile sensor assembly 244 comprises a housing 248.The housing 248 includes a base 250 having an attached base guide 258and a retainer 268. The low profile sensor assembly 244 also includes anupper slide member 252 supported for movement toward and away from thebase 250. Specifically, the upper slide member 252 is sized to slidablymove in an axial direction through a bore 262 of the base 250. Thesensor assembly 244 also includes a biasing member 256 extending betweenthe base 250 and the upper slide member 252. As in the preferredembodiment illustrated in FIGS. 1-4, the biasing member 256 employed inthe embodiment illustrated in FIGS. 5-7 is a coiled spring. The springbiases the upper slide member 252 away from the base 250. Furthermore,the upper slide member 252 includes a lower flange 296 extendingradially outward, and the base 250 includes an upper flange 298extending radially inward such that contact between the lower flange 296and the upper flange 298 limits the sliding axial movement of the upperslide member 252 within the base 250. The upper slide member 252includes a retainer 302 extending downwardly toward the base 250.

Also, in the preferred embodiment, the base 250 defines an inner guidesurface 294. The inner guide surface 294 is formed on the inner surfaceof the base guide 258, and it has a diameter slightly larger than thediameter of the lower flange 296 of the upper slide member 252. Theinner guide surface 294 substantially guides the lower flange 296 as itslides within the base 250, such that the upper slide member 252 slidesin a substantially axial direction. Thus, the lower flange 296 of theupper guide member 252 cooperates with the inner guide surface 294 ofthe base 250 to facilitate movement of the upper slide member 252relative to the base 250 in a substantially axial direction.

Additionally, as seen specifically in FIG. 5, the upper slide member 136includes a support wall 284 with a plurality of ridges 208 extendingradially outward therefrom. In the embodiment shown, there are fourridges 208, each spaced 90° apart from one another. The base 250 has acorresponding number of spaced grooves 210 located on the inner guidesurface 294. The grooves 210 are adapted to receive the ridges 208 suchthat the ridges 208 slide axially within the grooves 210, therebyinhibiting rotation of the upper slide member 252 relative to the base250 about the axis of the base 250. The sensor assembly 244 includes asensor 246 and emitter 304 of the type illustrated in the embodiment ofFIGS. 2 through 5. By inhibiting this type of rotation, the ridges 208and grooves 210 allow the sensor 246 to function more consistently andaccurately. It can be appreciated by one having ordinary skill in theart that the ridges 208 could be included on the base 250 while thegrooves 210 could be included on the upper slide member 252 withoutdeparting from the spirit of the invention.

Moreover, the low profile sensor assembly 244 includes an outer step276, which is adapted to accept the upper slide member 252 when theupper slide member 252 moves toward the base 250. Specifically, theouter step 276 is included on the retainer 268 of the base 250 and isaxially aligned with the lower flange 296 of the upper guide member 252.As shown in FIG. 7, the lower flange 296 can move into the space definedby the outer step 276 when the upper slide member 252 moves toward thebase 250.

The low profile sensor assembly 244 also includes a receptacle 306positioned at the axial center of the retainer 268 and aligned with theretainer 302 of the upper slide member 252. As such, when the upperslide member 252 moves toward the base 250, the retainer 302 can moveinto the receptacle 306.

Thus, the outer step 276 and the receptacle 306 each allow the upperslide member 252 to move further into the base 250, thereby allowing thelow profile sensor assembly 244 to collapse to a smaller height. In thisway, the low profile sensor assembly 244 is less likely to detrimentallyaffect the comfort level of the seat 10.

In summary, several features allow the low profile sensor assemblies 44,244 to collapse to a lower height. Namely, the intermediate guide member54, the outer step 76, 276, and the receptacle 106, 306, each allow theupper slide member 52, 252 to slide farther into the base 50, 250 forincreased collapsibility. As such, when the sensor assemblies 44, 244are incorporated into a vehicle seat assembly 10, the vehicle occupantis less likely to feel the sensor assemblies 44, 244 through the seatcushion 16. Thus, the low profile sensor assemblies 44, 244 are lesslikely to detrimentally affect the comfort level of the vehicle seat 10with which it is incorporated.

In addition, the structure of the sensor assemblies of the presentinvention facilitate primarily axial movement of the relevant componentsof the sensor assembly 44, 244 in response to a load on the seat cushion16. In this way, the sensor assemblies 44, 244 of the present inventionare not adversely influenced by shear forces that may also be generatedwhen an occupant is supported by the seat cushion 16.

As an alternative to the biasing member 56 and 256 illustrated in FIGS.2-7, the sensor assemblies 44, 244 may employ a variable biasing member,generally indicated at 356 in FIG. 8. As shown, the variable biasingmember 356 defines a first end 358 and a second end 360. The ends 358,360 can be of any type, including plain, squared, plain and ground, orsquared and ground. The variable biasing member 356 also includes aplurality of sections. Specifically, the variable biasing member 356shown includes a low rate section 362 adjacent each of the first end 358and the second end 360 and a high rate section 364 between the low ratesections 362. At least two of these sections 362, 364 have differentspring pitches and different spring rates. For instance, the low ratesections 362 each have a first spring pitch d1 and a first spring rate.The high rate section 364 has a second spring pitch d2 and a secondspring rate. The spring pitch d1, d2 and spring rate for each section362, 364 can be any suitable value. For instance, the first spring pitchd1 may be 1.60 millimeters with a spring rate of 0.25 N/mm, and thesecond spring pitch d2 may be 5.61 millimeters with a spring rate of1.51 N/mm in one embodiment. It should be appreciated by one of ordinaryskill in the art that the design of the variable biasing member 356 ischosen according to several factors including, but not limited to, thedesired biasing response of the member 356 and the manufacturability ofthe member 356. However, one skilled in the art will recognize that thedesign could vary without departing from the spirit of the invention.

The variable biasing member 356 can be incorporated into either of thesensor assemblies 44, 244 described above and used in place of thebiasing member 56, 256. As such, the variable biasing member 356 isoperatively disposed between the base 50, 250 and the upper slide member52, 252. Furthermore, the variable biasing member 356 supports the upperslide member 52, 252 and intermediate guide member 54, if included, formovement toward and away from the base 50, 250.

Turning now to FIG. 9, a graphical representation of the biasing forceversus the length of the variable biasing member 356 is shown. Thevariable biasing member 356 is adapted to bias the upper slide member52, 252 away from the base 50, 250 with a force that is non-linearlyrelated to movement of the upper slide member 52, 252 toward and awayfrom the base 50, 250. More specifically, point A represents a situationin which the vehicle seat assembly 10 is unoccupied. Once the seatassembly 10 becomes occupied, the variable biasing member 356 begins togenerate a biasing force within the sensor assembly 44, 244. Initially,the low rate sections 362 of the variable biasing member 356 deflect andgenerate a biasing force increasing along line L. Eventually, the lowrate sections 362 reach a solid height, represented by point B in FIG.9. Then, as the load on the sensor assembly 44, 244 continues toincrease, the high rate section 364 of the variable biasing member 356deflects and generates a biasing force increasing along line H. Theslope of line L is lower than the slope of line H because the springrate of the low rate sections 362 is lower than the spring rate of thehigh rate section 364. It is noted that the response of the variablebiasing member 356 graphically illustrated in FIG. 9 is onlyillustrative and does not limit the present invention. The variablebiasing member 356 could exhibit any non-linear response withoutdeparting from the spirit of the invention.

In the embodiment shown in FIG. 8, the variable biasing member 356 is astiffening, coiled compression spring made out of any suitable material,having any suitable free length, and having any suitable outsidediameter and wire diameter. In one embodiment, the variable biasingmember 356 is made out of stainless steel, has a free length of 25.00millimeters, and has an outside diameter of 15.30 millimeters and a wirediameter of 0.965 millimeters. Those having ordinary skill in the artwill appreciate, however, that the variable biasing member 356 may be ofany other suitable size and type, and may be made out of any othersuitable material without departing from the spirit of the invention.

As such, the variable biasing member 356 preferably exhibits anappropriate stiffness for both lighter and heavier occupants of thevehicle seat assembly 10. For instance, when a lighter occupant sits onthe seat cushion 16, the low rate sections 362 preferably deflect enoughsuch that the sensor 46, 246 detects a change in flux density from theemitter 104, 304 moving with the upper slide member 52, 252. However,when a heavier occupant sits on the seat cushion 16, the high ratesection 364 is preferably stiff enough to allow further deflectionwithout the biasing member 356 reaching a solid height. Thus, thevariable biasing member 356 allows data to be generated for lighteroccupants and for heavier occupants, thereby making the vehicle occupantsensing system 28 more responsive to a wider occupant weight range.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology, which has been used, isintended to be in the nature of words of description rather than oflimitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

1. A vehicle seat assembly comprising: a seat cushion defining an uppersurface and a lower surface spaced from said upper surface; and avehicle occupant sensing system including: a plurality of sensorassemblies, each of said sensor assemblies disposed below said seatcushion adjacent said lower surface, said sensor assemblies each havinga housing that includes a base and an upper slide member, said upperslide member moveable toward and away from said base and responsive tomovement of said upper surface of said seat cushion toward said lowersurface of said seat cushion thereby responding to the presence of anoccupant in said vehicle seat; a sensor operatively fixed relative to atleast one of said upper slide member and said base and operable todetect movement of said upper slide member toward and away from saidbase in response to the presence of an occupant in said vehicle seat;and a variable biasing member adapted to bias said upper slide memberaway from said base with a force that is non-linearly related tomovement of said upper slide member toward and away from said base,wherein said variable biasing member includes a plurality of sections ofwhich at least two of said sections exhibit different spring rates.
 2. Avehicle seat assembly as set forth in claim 1, wherein at least two ofsaid sections have different spring pitches.
 3. A vehicle seat assemblyas set forth in claim 1, wherein said variable biasing member includes alow rate section at each end and a high rate section between said lowrate sections.
 4. A vehicle seat assembly as set forth in claim 1,wherein said variable biasing member is a stiffening spring.
 5. Avehicle seat assembly as set forth in claim 1, wherein said variablebiasing member is a coiled spring operatively disposed between said baseand said upper slide member.
 6. A vehicle seat assemby as set forthclaim 1, wherein said sensor is operable to detect a change in magneticflux density generated by movement of said upper slide member toward andaway from said base.
 7. A vehicle seat assembly as set forth in claim 1,wherein said sensor assembly further comprises an intermediate guidemember disposed between said upper slide member and said base, saidintermediate guide member moveable toward and away from said base.
 8. Avehicle seat assembly as set forth in claim 1, wherein said upper slidemember includes a lower flange that defines the limit of movement ofsaid upper slide member away from said base, and wherein said lowerflange facilitates axial movement of said upper slide member relative tosaid base.
 9. A vehicle seat assembly as set forth in claim 8, whereinsaid base includes an inner platform that is adapted to accept saidlower flange of said upper slide member when said upper slide membermoves toward said base.